Numerous situations and/or scenarios exist in which wells are extended to subterranean locations in the earth's crust. For example, wells are drilled into subterranean formations in order to provide for the production of a variety of fluids, such as water, gas and/or oil; or for the injection of fluids, such as is employed in the secondary and tertiary recovery of oil (e.g., enhanced oil recovery). In many such situations and/or scenarios, in order to properly support the wall of the well, and possibly to exclude fluids from undesirably traversing the boundaries of at least some portions of the well, the well is cased with one or more strings of pipe, i.e., casing strings.
After a well has been drilled, the drillstring is withdrawn from the well and casing string is run into the well. Once the casing string is landed, the well is often conditioned by running a workstring into the well and circulating drilling fluid (i.e., mud) through the well to remove any residual drill cuttings. See, e.g., well completion operations such as described in any of the following: Peters, U.S. Pat. No. 3,455,387, issued Jul. 15, 1969; Kinney, U.S. Pat. No. 4,372,384, issued Feb. 8, 1983; Dillon et al., U.S. Pat. No. 5,346,007, issued Sep. 13, 1994; and Koplin, U.S. Pat. No. 3,312,280. Additionally or alternatively, wall scratchers are often run on the exterior of the casing string in order to scrape filter cake off the sides of the well wall in preparation for cementing (vide infra).
In order to complete the well, the casing must be bonded to the formation using a cementing procedure. Cementing procedures typically involve a drilling fluid displacement step, followed by a step of pumping a cement formulation (as a slurry) through the casing to the bottom of the well and then upwardly through the annular space between the outer surface of the casing and the surrounding wall structure, i.e., the formation. After the cement formulation is in place, it is allowed to set, thereby forming an impermeable sheath which, assuming that good bonding is established between the cement and the formation, and the cement and the casing, such bonding prevents the migration of fluids through the annulus surrounding the casing. The cement bonds further enhance the overall integrity of the well. For an example of a well cementing procedure, see, e.g., Parker, U.S. Pat. No. 3,799,874, issued Mar. 26, 1974.
Numerous cement formulations have been devised for a variety of applications and environmental conditions, but most are formulated with a desire to achieve adequate bonding at the interfaces of cement-formation wall and cement-casing. It is also desirable that such adequate bonding be uniformly established after a reasonable set or cure time, and that it endure for a sufficient period of time after the well has been completed and production begun. For examples of cement formulations used in the completion of oil and gas wells, see, e.g. Childs et al., U.S. Pat. No. 4,149,900, issued Apr. 17, 1979; Childs et al., U.S. Pat. No. 4,120,736, issued Oct. 17, 1978; Gallus, U.S. Pat. No. 4,069,870, issued Jan. 24, 1978; Gopalkrishnan, U.S. Pat. No. 5,262,452, issued Nov. 16, 1993; and Powers et al., U.S. Pat. No. 4,036,301, issued Jul. 19, 1977.
Notwithstanding the aforementioned desired characteristics of cement-derived bonding, bonding problems may nevertheless be encountered at the interface between the cement and the outer surface of the casing and the interface between the cement and the surrounding wall structure. This latter problem is particularly serious where the interface is provided by the wall of the well, i.e., the face of the formation exposed in the well. Accordingly, this interfacial bonding is typically evaluated prior to commencing with production.
To evaluate the cement bond to both the formation and the casing, a cement bond logging (CBL) procedure is used. Such procedures generally involve introducing into the well one or more tools as a package or sonde, wherein such a tool package or sonde is typically run up and down the well on a wireline. Most often, the cement bond logging tool associated with the sonde involves an acoustic means of interrogating the cement bond, whereby a sonic signal is produced and directed at the cement bond, and whereby one or more receivers and/or transducers receive a reflected signal that can be correlated with mechanical properties of the cement. See, e.g., Masson et al., U.S. Pat. No. 4,757,479, issued Jul. 12, 1988; Carmichael et al., U.S. Pat. No. 4,551,823, issued Nov. 5, 1985; and Jutten et al., “Relationship Between Cement Slurry Composition, Mechanical Properties, and Cement-Bond-Log Output,” SPE Production Engineering, February, 1989, pp. 75-82.
In addition to the above-mentioned CBL operations, logs are also typically run to ascertain structural integrity and geometry (e.g., pipe eccentricity) of the casing string along the length of the wellbore, as the geometry of the tubing can change during deployment operations. This type of log is often carried out concurrently with the CBL operations. See, e.g., Graham et al., “Cement Evaluation and Casing Inspection With Advanced Ultrasonic Scanning Methods,” Society of Petroleum Engineers, Annual Technical Conference Paper No. 38651, October 1997.
After cementing the casing in a well, one or more cleanout operations or procedures are typically employed to clean out the well in preparation for production. Such procedures can vary considerably, but often involve running a workstring down the well with one or more cleaning tools and/or devices attached to it. Such cleaning tools can include brushes, scrapers, drill bits (e.g., for drilling out cement plugs, etc.), and means for delivering (and circulating) fluids and/or chemicals to the wellbore for the purpose of cleaning out the cased wellbore (including cleaning of the drilling fluid contained therein) and/or the interior surfaces of the associated casing prior to drilling fluid displacement, perforation and subsequent production. See, e.g., Reynolds et al., U.S. Pat. No. 5,570,742, issued Nov. 5, 1996; Reynolds et al., U.S. Pat. No. 5,419,397, issued May 30, 1995; Reynolds, U.S. Pat. No. 6,758,276, issued Jul. 6, 2004; and Carmichael et al., U.S. Pat. No. 6,401,813, issued Jun. 11, 2002.
After such above-described cleanup operations, the drilling fluid present in the wellbore must be displaced by completion fluid, i.e., a displacement operation or procedure. However, the aforementioned cement bond logging is typically done in a separate step between the cleanup operations and the displacement operations. This requires removal of the workstring and the deployment of a sonde into the well on a wireline (vide supra).
While the abovementioned cement bond logging methods and cleanup procedures work adequately and ensure well integrity and well cleanliness before production begins, they require the steps of running a workstring down the well and, separately, running a wireline down the hole. This extra step of running a wireline (separately from the workstring) equates to considerable time expenditures that are justifiable, most identifiably, by the assurance such testing affords.
In view of the foregoing, an improved method and/or system for cement bond logging (and for logging/evaluating other aspects of the well casing and/or surrounding formation) and wellbore integrity assessments would be extremely useful—particularly wherein such a method and/or system provides greater efficiency with respect to completions operations. Furthermore, while the discussion which follows focuses primarily on oil and gas wells, those of skill in the art will appreciate that at least some of the method and system embodiments discussed herein can be extended to a variety of the situations/scenarios mentioned above.